Sai Counter (歳) - Japanese Ages
The Japanese age counter is 歳 (sai), often written 才 in casual contexts. The pattern is regular at most positions but irregular at 1 (is-sai), 8 (has-sai), 10 (jus-sai), and especially at 20 (hatachi はたち, totally irregular).
Age in years. Irregular at 1, 8, 10, 20.
| # | Kanji | Romaji | Notes | Audio |
|---|---|---|---|---|
| 1 | 一歳 | is-sai | ||
| 2 | 二歳 | ni-sai | ||
| 3 | 三歳 | san-sai | ||
| 4 | 四歳 | yon-sai | ||
| 5 | 五歳 | go-sai | ||
| 6 | 六歳 | roku-sai | ||
| 7 | 七歳 | nana-sai | ||
| 8 | 八歳 | has-sai | ||
| 9 | 九歳 | kyū-sai | ||
| 10 | 十歳 | jus-sai / jis-sai | ||
| 20 | 二十歳 | hatachi | totally irregular |
The hatachi irregularity
Twenty years old in Japanese is hatachi (はたち, written 二十歳), not ni-jus-sai. The form is a fossilised native Japanese reading, surviving from before Sino-Japanese readings displaced the native count above 10.
Twenty has cultural weight in Japan as the historical age of majority (until 1 April 2022, when majority was lowered to 18). The Seijin-no-hi (成人の日, Coming-of-Age Day) is still celebrated by 20-year-olds on the second Monday of January.
Sound-change pattern
- Gemination at 1, 8, 10: is-sai, has-sai, jus-sai (or jis-sai). The /s/ doubles after the preceding consonant.
- Regular at 2-7, 9: ni-sai, san-sai, yon-sai, go-sai, roku-sai, nana-sai, kyu-sai. No rendaku; no gemination.
- Totally irregular at 20: hatachi, not ni-jus-sai.
Asking and answering age
- Polite question: おいくつですか (o-ikutsu desu ka).
- More formal: お年はいくつですか (otoshi wa ikutsu desu ka).
- Casual question: 何歳 (nan-sai). Pair with a context-appropriate verb.
- Answer: 私は二十五歳です (watashi wa ni-jus-go-sai desu): “I am 25 years old”.
- For 20: 私は二十歳です (watashi wa hatachi desu).
Cultural ages worth knowing
- Hatachi (20): traditional age of adulthood. Seijin-no-hi celebration.
- Kanreki (還暦, 60): the “return-of-the-calendar” year, marking the completion of one full 60-year sexagenary cycle.
- Koki (古希, 70): from a Chinese poetic phrase “antiquity-rare seventy”.
- Kiju (喜寿, 77): the “joy age”, because the cursive form of 喜 (ki) resembles 七十七 (77).
- Beiju (米寿, 88): the “rice age”, because 米 (kome / rice) can be decomposed into 八十八 (88).
Frequently asked questions
Why is hatachi used instead of ni-jus-sai for 20?
Hatachi (はたち, 二十歳) is a fossilised native Japanese form for “20 years old”, surviving from the older Yamato number system. 20 has cultural weight in Japan as the age of majority (until 1 April 2022, when majority was lowered to 18; hatachi-no-iwai “celebration of turning 20” still happens at age 20). The form ni-jus-sai exists and is grammatically correct, but hatachi is the conventional reading for age 20.
What is 才 versus 歳 for age?
Both are read sai. 歳 is the standard / formal kanji used in official documents. 才 is a simpler form used in casual writing, advertisements, and on children's television. The reading is identical; the choice is register, not meaning. Some readers find 才 less formal.
Why is 1 year old is-sai, not ichi-sai?
Gemination. The /s/ doubles after the preceding 1 (ichi), producing is-sai. The same pattern appears at 8 (has-sai), 10 (jus-sai / jis-sai), and 20 in some traditional usage. NHK Pronunciation Dictionary specifies is-sai as standard.
How do I ask someone's age politely?
O-ikutsu desu ka (おいくつですか) is the polite form. Otoshi wa ikutsu desu ka (お年はいくつですか) is more formal still. Direct questions about age are considered slightly intrusive in Japanese conversation; use the polite forms unless context is casual.
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